For actively traded stocks, the price could be set by the means of the supply and demand. If there are more customers than vendors for a specific stock, the price will rise. If there are more sellers than buyers, the price will fall. They have an inverse relationship. The economy, politics, or any catastrophic events could be the basis whether there will be more customers or vendors for a specific stock. If the events are momentous, it could have effect on or involve the entire market and move it up or down.
Not actually, hahaha. I just read something about Daily stocks that's why I was able to post that. LOL
Some stock price could be manipulated most especially penny stocks, while others can't be easily only with change in policy and other methods which leads to inside trading. The answer to you question is quite broad really.